1. Field of the Invention
The present invention relates to an imaging system, and more particularly to an apparatus for look-up table mapping in a scanning system to improve efficiency in memory usage, furthermore, to apply to a real-time scanning system without loss accuracy of system.
2. Description of the Prior Art
Up-to-date, there are more and more applications about imaging systems, such as camera and scanner, etc.. As the computer technology and the like are getting more and more progress, it seems impossibly to fit human beings' desire. In recent years, the difference between the computer world and the real is fast vanishing, parts of it appears in imaging systems that images generated by an imaging system are from binary through gray-scales to color though people do not exactly feel this change that is happening each day.
Although it is a requirement that an imaging system is capable of imaging a picture in a manner with higher accuracy and resolution, more additional arithmetical operations are required to process such a great deal of image information. In a scanning system, there are lots of important tasks must be processed such as image processing, .gamma.-correction, and high-light shadow, etc.. It is impossible for a scanner to complete such a great deal of tasks in a short time interval only by using hardware implementations even if it contains a powerful CPU (central processing unit) of Pentium-series. It goes without saying that a scanner can complete them as a real-time system. There are some schemes for overcoming the difficulty. One famous method of them is to use a look-up table that it is known as a popular skill in this art. There stores predetermined mapping information in a look-up table that follows a curve (usually, a monotone curve is chosen), and acts as a memory to provide an output each time when it receives an address. All skilled in the art know that this method is flexible, fast, and easy to implement in a real time manner, however, its disadvantages in performance are seldom under our considerations. One of these disadvantages is, while an input signal has more bits than ever, and the size of look-up table will increase incredibly.
It is seldom over 10 bits for an output signal in a scanning system owing to the visual of human being is insensitive to detail color differences. Typically, 8 bits for each output signal is enough for displaying. While we increase the bits of an input signal that increases the size of look-up table it will also result a look-up table to contain a lot of redundant mapping terms. Using FIG. I to simply describe this situation: an input signal follows the format of 16-bits per pixel and 8-bits per pixel for an output signal. Clearly, about 256 input signals map into an identity mapping terms on an average, that is, about 255 mapping items seem redundantly in the table. Moreover, if we choose the traditional skill that uses only one look-up table, at least a 2.sup..noteq. .times.8 memory (that is, a 64 KBytes memory) is necessary for storing the mapping information. Obviously, we hardly can find an ASIC chip containing such a great deal of memory storage, up-to-date (although it should not remain a problem in the future). The present invention just suggests an improvement related to this disadvantage.